TCP quad: source IP, destination IP, source port, destination port. This thing determines a TCP connection. When the client connects to the server, it chooses the unused port as the source port.

the connection to the real data transfer is a new temporary communication port opened after the socket.accept () step.

it is not a new temporary port, but the client selects the source port first, and then initiates a connection to shake hands. Each TCP packet has a quad, so the server knows the port used by the client.

Port 80 is not usually used for real data transmission between the server and the client

it takes a TCP quad to determine a TCP connection, so there is no case of using only port 80 or a new port to transmit. Both source and destination ports are required and no new ports will be opened.

for example, take a look at a running redis (the same for http server), listening on port 6379:

the first LISTEN status is whether the ESTABLISHED behind the listening socket, is the socket of the socket,ESTABLISHED established by the client or the server or port 6379, but the client port is different.